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Fix IAR compiler endianness detection in alignment.h #838

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nzzlinh wants to merge 3 commits from nzzlinh/fix-iar-endianness into development
pull from: nzzlinh/fix-iar-endianness
merge into: gh-Mbed-TLS:development
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nzzlinh commented 2026-07-14 09:39:13 -05:00 (Migrated from github.com)

Description

This PR fixes a critical bug where the IAR compiler always triggers the Little-Endian code path, even when compiling for Big-Endian CPU. Fix https://github.com/Mbed-TLS/mbedtls/issues/10381

The IAR C/C++ compiler always defines both __LITTLE_ENDIAN__ and __BIG_ENDIAN__ macros internally, assigning '1' to the active endianness and '0' to the inactive one. The previous check defined(__BIG_ENDIAN__) always evaluated to true on IAR. This commit updates the check to verify the actual value: (__BIG_ENDIAN__ == 1).

image

References from IAR Development Guide for several MCU families

[1] ARM: https://wwwfiles.iar.com/arm/webic/doc/EWARM_DevelopmentGuide.ENU.pdf - p.494
[2] Renesas RX: https://wwwfiles.iar.com/RX/webic/doc/EWRX_DevelopmentGuide.ENU.pdf - p. 428
[3] Renesas RL78: https://wwwfiles.iar.com/rl78/EWRL78_DevelopmentGuide.ENU.pdf -p.389
[4] STM8: https://wwwfiles.iar.com/stm8/guides/EWSTM8_DevelopmentGuide.pdf - p.334

PR checklist

## Description This PR fixes a critical bug where the IAR compiler always triggers the Little-Endian code path, even when compiling for Big-Endian CPU. Fix https://github.com/Mbed-TLS/mbedtls/issues/10381 The IAR C/C++ compiler always defines both `__LITTLE_ENDIAN__` and `__BIG_ENDIAN__` macros internally, assigning '1' to the active endianness and '0' to the inactive one. The previous check `defined(__BIG_ENDIAN__)` always evaluated to true on IAR. This commit updates the check to verify the actual value: `(__BIG_ENDIAN__ == 1)`. > <img width="627" height="94" alt="image" src="https://github.com/user-attachments/assets/af07401f-62ea-4990-ab5a-a951b0ee4b8f" /> ### References from IAR Development Guide for several MCU families [1] ARM: https://wwwfiles.iar.com/arm/webic/doc/EWARM_DevelopmentGuide.ENU.pdf - p.494 [2] Renesas RX: https://wwwfiles.iar.com/RX/webic/doc/EWRX_DevelopmentGuide.ENU.pdf - p. 428 [3] Renesas RL78: https://wwwfiles.iar.com/rl78/EWRL78_DevelopmentGuide.ENU.pdf -p.389 [4] STM8: https://wwwfiles.iar.com/stm8/guides/EWSTM8_DevelopmentGuide.pdf - p.334 ## PR checklist - [x] **changelog** provided - [x] **framework PR** not required - [x] **TF-PSA-Crypto development PR** provided (this PR) - [x] **TF-PSA-Crypto 1.1 PR** https://github.com/Mbed-TLS/TF-PSA-Crypto/pull/845 - [x] **mbedtls development PR** not required because: fix is isolated to TF-PSA-Crypto core - [x] **mbedtls 4.1 PR** not required because: fix is isolated to TF-PSA-Crypto core - [x] **mbedtls 3.6 PR** https://github.com/Mbed-TLS/mbedtls/pull/10840 - [x] **tests** not required because: we don't have IAR in our CI
gilles-peskine-arm (Migrated from github.com) reviewed 2026-07-14 09:39:13 -05:00
nzzlinh commented 2026-07-14 09:59:01 -05:00 (Migrated from github.com)

Related issue in MbedTLS repo: https://github.com/Mbed-TLS/mbedtls/issues/10381

Related issue in MbedTLS repo: https://github.com/Mbed-TLS/mbedtls/issues/10381
gilles-peskine-arm (Migrated from github.com) reviewed 2026-07-20 08:59:00 -05:00
gilles-peskine-arm (Migrated from github.com) left a comment
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LGTM on code reading. (I haven't tested because I don't have a big-endian arm testing environment readily available, and I do have access to IAR for arm but the license server is down at the moment.)
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git switch 'development'
git merge --no-ff 'nzzlinh/fix-iar-endianness'
git switch 'nzzlinh/fix-iar-endianness'
git rebase 'development'
git switch 'development'
git merge --ff-only 'nzzlinh/fix-iar-endianness'
git switch 'nzzlinh/fix-iar-endianness'
git rebase 'development'
git switch 'development'
git merge --no-ff 'nzzlinh/fix-iar-endianness'
git switch 'development'
git merge --squash 'nzzlinh/fix-iar-endianness'
git switch 'development'
git merge --ff-only 'nzzlinh/fix-iar-endianness'
git switch 'development'
git merge 'nzzlinh/fix-iar-endianness'
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